This invention relates to an improved optical time delay system based on switchable diffraction gratings and a White Cell geometry. The use of the switchable diffraction gratings in the form of switchable transmission gratings and switchable volume holographic mirrors adds a reliable electro-optic switch technology with low insertion loss, low crosstalk, and high reliability to relatively compact White Cell based time delay systems.
White Cell geometries have been previously used for time delay systems. In the original White cell, light bounces back and forth repeatedly between three spherical mirrors, all identical, and is focused to a new spot on every bounce. A number of proposed systems use a White Cell multi-pass approach in conjunction with spatial light modulators, deformable mirrors, and MEMS-type spatial light modulators. However, existing art is limited in application to phased array beamforming due to lifetime issues. For example, a phased array antenna that steers a beam at a kilohertz rate requires more than 31.5 billion time delay reconfigurations per year. For systems utilizing MEMS devices, pointing stability of the mechanically deflected mirrors is an issue. Also for systems using moving parts (such as MEMS) reliability and repeatability are concerns.
Therefore, there is a need for an electro-optic White Cell based optical time delay system that has no moving parts.
Further more, there is a need for a time delay system that exhibits improved long-term stability.